Project Summary Hibernating ground squirrels have dramatically decreased heart rates (3-5 beats per minute) and blood flow, which should put them at risk of forming blood clots. However, they actually have several adaptations during hibernation that prevent blood clotting, including 3-fold decreases in clotting Factors VIII (FVIII) and IX (FIX), and 10-fold decreases in von Willebrand factor (vWF), neutrophils, and platelets. Decreases in all four of these blood components lead to bleeding disorders in humans, namely hemophilia A and B, von Willebrand disease and thrombocytopenia or low platelet counts. The Central Hypothesis of this proposal is that ground squirrel platelets are resistant to cold storage lesions, most likely through a combination of decreased clearance, apoptosis, and activation in the cold. This adaptation could be reflected in differential protein expression, signaling, and ligand binding of ground squirrel platelets stored in the cold either in vitro or in situ. In previous research, we have found that platelets from hibernating ground squirrels bind less to vWF and collagen under flow, yet remain able to be activated by agonists. The three Specific Aims of this proposal are to 1) measure impact of in vitro and in situ cold storage on platelet adhesion and clearance, 2) determine the effects of in vitro and in situ cold storage on platelet proteomics, and 3) measure effect of in vitro and in situ cold storage on platelet apoptosis and signaling. This project is innovative because we use ground squirrels with natural adaptations to extreme physiological stresses on their cardiovascular system to study resistance to cold storage lesions in platelets. This research could lead to medical advances to treat thrombocytopenia, store human platelets in the cold for transfusions, and regulate blood coagulation in cases of accidental or induced hypothermia.